The long-term career goal of the candidate is to understand the as yes undefined mechanisms of megakaryopoiesis and platelet production and to apply the insights to understand and possibly treat hematological disorders. Megakaryopoiesis is a complex process in which bone marrow megakaryocytes give rise to circulating platelets. Microtubule cytoskeleton has a unique organization in megakaryocytes which is essential for normal platelet production. The overall objective of this project is to investigate the role of stathmin, a major microtubule-regulatory protein, in the process of polyploidization (i.e. acquisition of more than 4N DNA content) and platelet production in primary megakaryocytes. Stathmin is physiologically downregulated during megakaryopoiesis and is absent in platelets. The levels of stathmin expression correlate inversely with megakaryocytes polyploidization. Inhibition of stathmin increases ploidy while its overexpression decreases ploidy of megakaryocytic cell lines. Based on this, our hypothesis is that downregulation of stathmin expression is necessary for polyploidization and platelet production during normal megakaryopoiesis. Thus, we propose to prevent physiological downregulation of stathmin in primary megakaryocytes and platelets ex vivo and in vivo in transgenic mice study the effects of this intervention on polyploidization and platelet production. First, we will investigate the effects of lentivirus-mediated overexpression of stathmin on polyploidization and the potential mechanisms underlying this process (Specific Aim 1). Second, we will generate transgenic mice that overexpress stathmin conditionally in megakaryocytes (Specific Aim 2). Third, we will investigate megakaryopoiesis and platelet formation in transgenic megakaryopcytes (Specific Aim 3). These studies should make it possible to better understand the process of normal megakaryopoiesis and provide the basis for the future investigation of the potential role of stathmin and/or microtubules in abnormal megakaryopoiesis and platelet production. They should also make possible to validate the potential use of microtubules as therapeutic targets in platelet disorders.